Magneto-optical disc drive data storage devices, or magneto-optical drives, are well known in the industry. Such devices utilize a combination of electromagnetic and optical light technologies to store and retrieve data on the surface of appropriately designed plastic discs.
Evolutionary advances in the disc media and read/write heads have lead to the present generation of magneto-optical disc drives which are capable of storing large amounts of data on one side of a single disc. In order to achieve such data capacities, the magneto-optical transducers used to record and retrieve data are incorporated in self-acting hydrodynamic head assemblies that fly above the discs on a thin layer of air dragged along by the spinning disc. Head assemblies of the current generation typically fly at heights above the disc that bring the operative component of the magneto-optical transducer to within approximately 4 microinches (0.000004 inch) of the media surface.
"The magneto-optical head assembly is commonly mounted to an actuator which is capable of controllably moving the head assembly to any desired one of a plurality of data tracks on the disc surface. The most common type of actuator currently in use is a rotary type which includes a pivot shaft located near the outer periphery of the disc and extending normal to the plane of disc rotation. An actuator body is mounted to the pivot shaft via an arrangement of precision ball bearings. One side of the actuator body is connected to a motor which provides the motive force necessary to rotate the actuator body, and a second side of the actuator body provides a mounting system for attaching the rotatable actuator body to the magneto-optical head assembly, as well as a system of lenses or fiber-optic elements for directing light to and from the magneto-optical transducer on the head assembly.
As mentioned above, the head assembly typically includes an arrangement of self-acting hydrodynamic air bearing surfaces which interact with a thin layer of air dragged along by the surface of the spinning disc. The interaction between the air bearing surfaces of the head assembly and the spinning disc produces a lifting force which tends to lift the head assembly away from the disc surface.
It is well known in the industry to mount the head assembly to the actuator body via a head suspension, commonly formed of a thin, flexible stainless steel foil. Besides providing a physical mounting apparatus for the head assembly, the head suspension also typically includes a spring portion, a rigid beam portion and a gimbal portion. The head assembly is mounted to the gimbal portion, which also provides compliance in the roll and pitch axes of the head assembly, to allow the head assembly to follow minor variations in the surface of the disc. The spring portion of the head suspension produces a load force used to balance the hydrodynamic lifting force of the air bearing surfaces of the head assembly. This load force is transferred from the spring portion to the gimbal portion--and thus to the head assembly--by the rigid beam portion of the head suspension.
It is also common to localize the application of the load force to the head assembly by providing a precisely located feature on the gimbal portion of the head suspension, such as a stamped dimple. The exact location at which the load force is applied to the head assembly is referred to as the load point, and this load point is typically selected in relationship to the overall head assembly to act in cooperation with the air bearing surfaces of the head assembly and cause the head assembly to fly at a desired attitude in relationship to the disc surface."
While improvements to the surface quality of magneto-optical discs are being made, typical magneto-optical discs of the current generation still include media defects, or asperities, that are large enough to cause direct contact between the head assembly and the disc. Such contacts can result in excitation and vibration of the head assembly, which can lead in turn to uncontrolled variations in the spacing between the data transducer in the head assembly and the disc surface. Spacing variations of this type can produce undesirable modulation of the read/write signals and degradation of the data recording and/or recovery capability of the disc drive.
A need clearly exists, therefore, for a magneto-optical head assembly which can withstand contact with disc asperities without being subject to vibration-induced read/write signal modulation.